


Hypothesis

by Jaela



Category: Free!, Haikyuu!!
Genre: Crossover, Crossover Pairings, Kissing for science, M/M, Polyamory
Language: English
Status: Completed
Published: 2017-09-03
Updated: 2017-09-03
Packaged: 2018-12-23 05:40:30
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,359
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/11983329
Author URL: https://archiveofourown.org/users/Jaela/pseuds/Jaela
Summary: Tsukishima Kei takes another summer trip to Iwatobi. Hazuki Nagisa is learning about the scientific method.





	Hypothesis

**Author's Note:**

> Shiptember, Day 2! I like sports crossover ships, especially if they involve Nagisa. So here's NagiTsukki sharing a little more than just their mutual favourite food!
> 
> Originally written for SASO2016's Bonus Round 1, for this prompt: http://sportsanime.dreamwidth.org/13489.html?thread=4624561#cmt4624561

“Buy me cake, Kei-chan,” Nagisa says. His eyes are big and round and innocent, which is the most dangerous way for someone this devious to look.

“No, Hazuki.”

“It’s  _Nagisa-chan,_ we’re not strangers!”

Nagisa is expecting the following compromise: that Kei will refuse the  _–chan_  part and default back to just  _Nagisa._  Kei is one step ahead of him.

“Quit it with  _Kei-chan_ , and stop mooching,” he says, “and I’ll reconsider your first name privileges.”

“Mean,” Nagisa mumbles.

“You knew that from the beginning,” Kei reminds him, “and yet you always come and find me the minute I get here.”

Nagisa hums to himself and considers that. “I think you used to be nicer.”

“You’re remembering wrong. I’ve always been like this.”

“Really?”

Kei isn’t sure why they’re even friends.

They met three summers ago, during a summer visit by Kei’s family to see his aunt’s new home in this weird little fishy-smelling port town in Tottori. That first trip had only been a weekend, but Kei’s mother had been so charmed by the place that by now, they stay a full week when they come here.

“That’s a question you can only answer for yourself,” Kei says as he pushes open the door to the bakery.

Nagisa is already past that topic, though. “I thought we weren’t getting cake.”

Kei shrugs. “I said no to buying it for you. I didn’t say anything about getting some for myself.”

“So cruel!” Nagisa whines, crouching in front of the display case even though he knows the menu by heart. The woman at the counter just smiles indulgently, because she knows Nagisa. Everyone employed here knows Nagisa. He’s a familiar presence by now, and so is his drama.

“It’s cheaper if you buy two slices,” Nagisa says. His breath is fogging up the glass.

“I can’t eat two.”

“I can! I can eat twice that much, at least!”

“Good for you,” Kei says. “Buy your own cake, Nagisa.”

He says the name with a warning tone, as a reminder that hearing it is conditional upon Nagisa’s behavior.

“I spent my allowance already,” Nagisa admits, standing up with resignation weighing his shoulders down. He can no longer stare at the pretty things he can’t have.

“On what?” Kei points out the cake slice he wants to the cashier, who seems intent on not interrupting. She nods and boxes it up for him.

“Clothes,” Nagisa says. Which  _sounds_  practical, but Kei has witnessed the way Nagisa impulse buys any clothing item he sees with a penguin motif. Which is a lot, because this is a town where penguin merchandise is only outnumbered by squid merchandise.

Kei pays in exact change for his purchase, and lifts the box delicately with both hands. The only way to handle precious cargo.

“That’s good,” he says. “It’ll last longer than cake.”

“Can’t eat a shirt, though,” Nagisa laments on their way out.

“Maybe if you try hard and believe in yourself.”

Nagisa giggles, for all the world like the joke wasn’t at his expense. Kei likes that about him, maybe—that Nagisa appreciates a well-timed dig no matter who’s on the receiving end. Nagisa takes Kei to a secluded spot up on a hill—a pretty view of the ocean, but high up enough that the smell of fish isn’t too strong. Nagisa knows his stuff when it comes to proper cake-eating locales. Kei likes that about him too, maybe.

“Hey, let me have some.”

“Hazuki,” Kei responds, because he can.

“Fiiiiiine.” Nagisa slumps on the ground next to Kei. His round face looks even rounder when he presses his chin into his hand and puffs out his cheeks, all petulant. “But what am I gonna eat now?”

“You don’t have to be eating at all times,” Kei says in between bites of cake. He eats slowly, savoring each bite. Because it deserves to be enjoyed, but also to prove a point, because Nagisa is going to have to learn patience and decorum at some point in his life.

“You’re a lot like my boyfriend,” Nagisa says out of nowhere.

Kei stares. He’s gotten over the shock that Nagisa  _has_  a boyfriend now—a detail he first casually alluded to this morning, like it was nothing—but Kei had thought maybe than would mean Nagisa easing up a little on his usual flirting. Instead Nagisa is staring at him with fond, sparkling eyes, and smiles in a way that Kei has had practice in blatantly ignoring.

“Really.”

“Sure! Kei-chan and Rei-chan,” Nagisa singsongs, hugging his knees and tapping his feet against the ground. “You’re both tall and you both wear glasses. Well—you’re  _really_  tall, though.”

“You’re just short,” Kei says. A libero, in a different world, if Nagisa had chosen volleyball instead of the swim team he gushes about nearly as often as he breathes.

“Plus, you do everything all…  _just so_ , like there’s an exact way you’re supposed to do it.” Nagisa imitates Kei raising the cake fork to his mouth and taking a small, precise bite. “Rei-chan does this thing where he tilts his chin  _juuuuust right_  when we kiss so he doesn’t bump his glasses. That way he doesn’t have to take them off.”

Kei feels fidgety and uncomfortable, but he wrestles the feeling back. If he snaps at Nagisa and tells him not to talk about kissing his boyfriend, that’s exactly the thing Nagisa will talk about all the time when he wants to gain some kind of advantage. Better to just ignore it and show no weakness. Let it pass.

“I want to conduct an experiment,” Nagisa announces, changing the subject. Ah, and this is why they are friends, Kei supposes—because when Kei utters those exact words, Nagisa nods earnestly and goes along with whatever Kei says next, no matter what it is. It’s nice to have that, when he’s here. Makes the stay less boring. Less lonely, he might say, if he had any interest in being honest with himself about it.

“Hypothesis?” Kei asks.

Nagisa wrinkles up his nose, the way he does at technical terms from any subject besides history. Kei likes science, though, and he’s been slowly selling Nagisa on it by way of killing time with casual social experiments.

“It’s a secret,” Nagisa says. “It has to do with kissing.”

Okay, so this wasn’t a change of subject after all. “You can’t conduct an experiment on your boyfriend when he’s not even here,” Kei says, fighting hard against that fidgety feeling again. “And I’m not helping, especially not for a  _secret hypothesis._  Go by yourself.”

“I already did his part,” Nagisa says. “And—okay, fine. The hypothesis is that boys with glasses are good kissers. You’re the… control group?”

“Wrong,” Kei says, though at least an effort was made. “I’m not a group, and I can’t be the control if there’s a part of the experiment I wasn’t involved in.” Kei isn’t sure why he’s even explaining, except maybe that it’s just better than facing what Nagisa is getting at.

“What’s the control, then? This stuff is hard to remember.”

“It depends on how you’re testing your hypothesis.”

“Oh! By kissing Kei-chan.”

Of course. Kei doesn’t like this view of the ocean so much anymore. “The presence of glasses, for one.” The cake doesn’t even look as appetizing. Why is he still explaining? “You, for another.”

“Oh, right,” Nagisa says. “You’re a variable.”

“Everything is a variable.” Kei stabs his fork into the strawberry and just leaves it standing there. “It doesn’t matter, though. I’m not helping you cheat on your boyfriend.”

“It’s not  _cheating,_ ” Nagisa says, giving Kei a look like he’s suggested something absurd. “We kiss other people sometimes.” Which  _is_  absurd. “I’ll just text him and ask first. It’s fine.”

About twice per summer, Nagisa manages to get a picture of Kei before he can dodge out of the frame. He catches one now, and starts tapping away on his phone cheerfully.

“Nagisa.”

“Hold on, let me concentrate.” Nagisa stares hard at the screen, tongue poking out of the corner of his mouth. He’s designing an elaborate kaomoji, which is something Kei is sort of irritated at himself for knowing. But, well, he’s received them often enough. “Okay, sorry, what were you saying?”

“That I’m not going to kiss you.”

“But it’s okay!” Nagisa says. His phone chirps. “Rei-chan  _says_  it’s okay, look!”

Kei turns his face away, but surreptitiously glances at the phone anyway. Sure enough, Nagisa’s request is accompanied by a kissy-face emoticon throwing flowers and hearts into the air. It also refers to Kei as a  _childhood friend_ , which is pushing the limits of what that term entails. When he thinks about it, though, Kei does feel as though they were just kids when he and Nagisa met.

The reply reads,  _It is fine. Please notify me beforehand if you think it will go further than kissing._

Kei does not know what to make of this. He is apparently ‘a lot like’ this guy he only knows by a few affectionately-delivered anecdotes from Nagisa, and now from a very formal-sounding text message permitting Nagisa to kiss, and possibly  _go further,_  with someone else. Someone this ‘Rei-chan’ has never met.

“Isn’t there someone else you should be asking for permission?”

“Huh?” Nagisa blinks. “Oh! Kei-chan, can I please kiss you to test my scientific hypothesis?”

Kei sighs. Weird things always happen when he comes here, and seem like a dream after he returns home. Weird things happen with Nagisa, the only waking remnant of the summer trips, who exists in between them in the form of intermittent and often-misspelled text messages.

Nagisa has never been dating anyone before. Kei has the impression Nagisa  _has_  wanted to kiss him before, though. Kei almost beat him to it once, before thinking better of it.

Kei is tired, and he has a half-finished piece of cake in a box on his lap, and he doesn’t feel like thinking better of it this time.

“Your hypothesis is flawed,” he says. “But if you’ll stop calling me Kei-chan, you can go ahead and test it.”

“Yay!” Nagisa scoots up close to him and folds his arms on top of Kei’s shoulders.

Kei frowns. Nagisa is flighty, scattered, and acts childish for reasons Kei can’t fully understand. He gets excited far too easily, which strikes a nerve for reasons Nagisa probably doesn’t understand. But when Kei kisses him, Nagisa lets him do it slowly, with the proper control required for a task so delicate. He follows Kei’s lead with the kind of restraint he wouldn’t have thought Nagisa possessed at all. It’s warm, sharing space and breath. Kei likes that, but he’s not so sure he likes the way it feels like his fingers aren’t getting proper circulation. He flexes them against the patchy grass, and loses focus for just long enough that his glasses bump against Nagisa’s nose. He goes for a deeper angle, something caustic but not altogether unpleasant flaring up inside him at the thought that he knows what Nagisa meant now, about the thing with his boyfriend—but he can’t think about it for long, because Nagisa is shifting his arms to drape them around Kei’s neck now. That’s even warmer, and it’s unexpectedly easy from there to leverage his hand on Nagisa’s leg and turn in to face him better, test the slide of his tongue against Nagisa’s, swallow up the soft sounds Nagisa starts to make. It’s all so intuitive, actually, which is a pleasant surprise. It’s also a lot to take in, though. Kei strokes a thumb over Nagisa’s jaw a few times, then uses that hand to pull Nagisa off of him.

Where Kei feels faintly dazed, a gauzy curtain pulled over his consciousness, Nagisa looks bright and alert and vibrant. His cheeks are so pink. Kei pinches one of them.

“Observations?”

Nagisa giggles and tightens his arms around Kei’s neck. “Tastes like strawberry shortcake!”

Kei scoffs, and takes off his glasses to polish them on his shirt. “You were just trying to get me to share.”

“Nuh uh. I was being scientific! That part was just a bonus.”

Kei’s glasses are clean. He keeps polishing them. “Uh huh. Conclusion?”

“I was right!” Nagisa relinquishes his hold on Kei to stretch his arms above his head, first one and then the other. He is alive with triumph.

“You’ll have to throw out the results anyway,” Kei says, and puts his glasses back on in the hopes that maybe it’ll distract from any evidence of his warming cheeks. Nagisa just pronounced him a good kisser. He tries not to think about it. “Your methods were flawed from the start. Too many inconsistencies, too small a sample size. It doesn’t hold up.”

“Hmm.” Nagisa leans his head against Kei’s shoulder. Kei tries to see what his face is doing, but Nagisa is so short that all he sees is a mess of hair. “It was fun, though.”

Kei doesn’t say anything. He feels on edge when he realizes his silence could be taken as agreement. But he doesn’t want to  _dis_ agree either.

“Are you going to finish that?” Nagisa runs one finger over a corner of the box. Kei eats a large forkful of cake—he’s still not really hungry anymore, but it’s the principle of the thing. On cue, Nagisa whines and rubs his head against Kei’s shoulder.

Kei keeps eating.

“Hey,” Nagisa says. “Would you do it again?”

“Hm.” Kei is still chewing.

“But like… not for sciencey reasons. Just because I like kissing you.”

“Hm.” Kei has swallowed. He just doesn’t know how to answer.

Nagisa lifts his head and looks at Kei with a gentle smile, still kind of rosy in the face. A little shy. Kei isn’t easy to fool, and he knows Nagisa’s tricks, and this seems genuine.

“Not right now,” is what Kei finally settles on.

“Okay, but. Sometime?”

Kei eats his strawberry, even though there’s still a little square of cake left and he usually saves the strawberry for last. He pushes the box into Nagisa’s lap.

“Sometime, I guess. Sure.”


End file.
